About 20 million metric tons of cotton fiber is produced annually worldwide with the U.S. producing about 20% of this. Approximately 16 million acres of cotton are planted in the U.S. representing one-seventh of the world acreage. The United States generates one fifth of the worldwide cotton fiber production, valued at about four billion dollars annually. Cotton is the premier natural fiber and provides excellent wearability and aesthetics. Although consumers prefer cotton, man-made fibers have captured a major share of the textile market while the market share of cotton is decreasing.
In order for the market share of cotton to increase, cotton fiber quality must be improved. Specifically, improvements in cotton fiber strength, the chemical reactivity for dye binding, water absorption and thermal properties are desirable for textile and other industrial applications. In the past, cotton fiber quality has been improved by classical plant breeding; however, this approach is seriously limited by species incompatibility and available traits. An alternative approach is to introduce foreign genes to confer desired traits into cotton via genetic engineering. Recently, John and Keller (1996) have reported expression of polyhydroxy butyrate polyester in cotton fiber, which has similar physical and chemical properties as polypropylene. This is the first report of a foreign gene expression in cotton fiber.
Cotton fiber or seed hair is a terminally differentiated single epidermal cell made up of primary and secondary cell walls, consisting primarily of cellulose (90%) and other compounds like hemicellulose, pectins and proteins. During the early stages of fiber development, the fiber cell elongates up to 3 cm over a period of 20 days post anthesis (DPA). The primary wall is about 100-200 molecules in thickness and consists of 30% cellulose and other polysaccharides, waxes and proteins (John and Keller, 1996). The secondary wall is made up of cellulose that is deposited during the third developmental stage, 16-45 DPA. Maturation of the fiber occurs 45-50 DPA, resulting in changes in mineral content and protein levels. The chemical composition and microstructure of primary and secondary walls influence properties like chemical reactivity, thermal characteristics, water absorption and fiber strength (John 1995b), which are important for the manufacturing of textile products. Therefore, it is highly desirable to synthesize a biopolymer within the fiber lumen without altering fiber wall integrity; this should result in sheltering the biopolymer within the cellulose walls (John and Keller, 1996).
We propose here to introduce a protein based polymer (PBP) from a synthetic gene into cotton that could increase fiber strength, alter thermal and water absorption qualities as well as enhance elasticity and dye binding capacity of cotton fiber.